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| 阿尔金造山带南缘岩浆混合作用:玉苏普阿勒克塔格岩体岩石学和地球化学证据 | |
| 引用本文： | 王超,刘良,张安达,杨文强,曹玉亭.阿尔金造山带南缘岩浆混合作用:玉苏普阿勒克塔格岩体岩石学和地球化学证据[J].岩石学报,2008,24(12):2809-2819. |
| 作者姓名： | 王超 刘良 张安达 杨文强 曹玉亭 |
| 作者单位： | 1. 大陆动力学国家重点实验室(西北大学),西北大学地质学系,西安,710069;西安地质矿产研究所,西安,710054 2. 大陆动力学国家重点实验室(西北大学),西北大学地质学系,西安,710069 3. 大庆油田有限责任公司勘探开发研究院,大庆,163712 |
| 基金项目： | 国家自然科学基金项目(40572111,40472043)和国家973项目(2009CB825003)资助 |
| 摘 要： | 阿尔金造山带南缘玉苏普阿勒克塔格岩体中的似斑状中粗粒黑云钾长花岗岩发育有岩浆成因的暗色包体,并且该花岗岩被花岗细晶岩呈脉状侵入。该岩体含有丰富的岩浆混合作用特征: 如暗色包体中的碱性长石斑晶、针状磷灰石、长石的环斑结构、石英/斜长石主晶和榍石眼斑等。暗色包体、寄主花岗岩和花岗细晶岩代表了岩浆混合演化过程中不同端元比例混合的产物。地球化学特征上,钾长花岗岩和暗色包体的主要氧化物含量在Harker图解中多呈线性变化。暗色包体主要为闪长质,MgO、K2O含量高,为钾玄岩系列,总体上高场强元素不亏损,显示了岩浆混合中的基性端元信息,可能为幔源熔体结晶分异或壳幔物质的混合产物。寄主花岗岩均为准铝质,富碱,为高钾钙碱性系列,亏损Nb、Ta、Sr、P、Ti等高场强元素,高K2O/Na2O,富集高不相容元素,Ga含量高,显示了A型花岗岩的特征,Th/U 和Nb/Ta比值分别介于为6.67~10.96、8.99~11.94,代表了下地壳源区。花岗细晶岩均为钠质、过铝质,TiO2、MgO含量低, Na2O和CaO含量高,具有混合岩浆侵位后分异的特征。岩相学和地球化学特征说明岩浆混合作用对于环斑结构花岗岩的形成起到重要作用。花岗细晶岩中环斑长石的斜长石外环与钾长石内核的厚度比大于钾长花岗岩中的环斑长石,指示混合岩浆在一定的减压条件下更有利于环斑结构的形成。玉苏普阿勒克塔格岩体中的钾玄质暗色包体、高钾钙碱性花岗岩和中钾钙碱性花岗细晶岩代表了岩浆演化不同阶段的产物,反映了一个幔源岩浆和下地壳不断相互作用,引起地壳连续伸展减薄的过程,指示阿尔金南缘在早古生代末期存在造山后伸展背景下的幔源岩浆底侵作用。同一岩体中两种不同时代岩性的环斑结构显示了该岩体形成历史中的一定时空演化关系,代表了伸展过程中不同阶段的产物。 |
| 关 键 词： | 环斑结构 不平衡结构 暗色包体 岩浆混合作用 玉苏普阿勒克塔格岩体 阿尔金 |
Geochemistry and petrography of Early Paleozoic Yusupuleke Tagh rapakivi-textured granite complex, South Altyn: An example for magma mixing |
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| WANG Chao,LIU Liang,ZHANG AnD,YANG WenQiang and CAO YuTing.Geochemistry and petrography of Early Paleozoic Yusupuleke Tagh rapakivi-textured granite complex, South Altyn: An example for magma mixing[J].Acta Petrologica Sinica,2008,24(12):2809-2819. | |
| Authors: | WANG Chao LIU Liang ZHANG AnD YANG WenQiang and CAO YuTing |
| Institution: | State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China;State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China;Exploration and Development Research Institute of Daqing Oilfield Company Limited, Daqing 163712, China;State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China;State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China |
| Abstract: | The calc-alkaline granites of the Yusupuleke Tagh batholiths are associated with abundant mafic magmatic enclaves (MME) and aplite dikes. The granitc complex exhibits excellent evidence for magma mixing and mingling, such as the K-feldspar megacrysts in MME, long prisms of apatite, rapakivi feldspars (plagioclase-mantled K-feldspars), oikocrysts of quarts and feldspar-sphene ocelli. These suggest that mixing process of granitic and more mafic magmas induce the formation of the rapakivi texture. Textural evidence of the rapakivi magmas is better preserved in aplite than in the more deep-seated rapakivi granites formed by slow cooling, that indicate the decompression during crystallization of the magmas may promote the production of the mantled alkali feldspar megacrysts. Geochemical, there are linear arrays in binary diagrams. MME and host granitoids are considered cogenetic, and are hybrid rocks that were produced by the mixing of two components in different proportions. The granites are characterized by high Ga/Al, K2O/Na2O, Fe/Mg and low CaO, and showing A-type granite signatures but the aplites are peraluminous, high Na2O, CaO, similar to more felsic, fractionated A-type granites. Chemical data suggest that the MME originated from the enriched mantle melts, whereas the felsic component was produced by partial melting of preexisting crustal materials. Deep-seated interactions between felsic and mafic magmas were responsible for the common characteristics of both magma suites. The chemical evolution of post-orogenic plutnism indicates mantle-crust interactions at decreasing depths in an actively extending orogen. The distinct composition and rapakivi-texture of the granitoids reflects two stages of hybridization and emplacement at the end of an orogenic cycle. |
| Keywords: | Rapakivi texture Disequilibrium texture Mafic microgranular enclaves Magma mixing Yusupuleke Tagh granite complex Altyn |
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